Japanese Patent Publication No. 3-47359 discloses a method of manufacturing a conventional hard roll employing cast molding.
First, a fibrous material impregnated with thermosetting resin is wound on the outer peripheral surface of a metal roll core for forming a fiber-reinforced under winding layer.
Separately from the aforementioned step, a thermosetting synthetic resin material containing a filler is cast into a cylinder forming mold of a prescribed size and hardened at a prescribed temperature for forming an outer layer cylinder.
The metal roll core having the fiber-reinforced under winding layer is covered with the outer layer cylinder, and an adhesive having low viscosity is cast into an annular clearance defined between the under winding layer and the cylinder and hardened at a prescribed temperature, for joining and integrating the under winding layer and the cylinder with each other through an adhesive layer.
The aforementioned cylinder forming mold is vertically fixed.
The conventional method of manufacturing a hard roll has the following problems: While the outer surface and the inner surface of the formed cylinder are cut for attaining cylindricity, the surface of the formed cylinder is waved in the case of a large-sized roll used in the paper industry, and hence a large cutting margin must be provided in consideration of allowance. Therefore, the yield is disadvantageously deteriorated.
Further, it is difficult to remove voids when forming the outer layer cylinder.
In addition, bad influence is exerted on the quality of an objective product processed with the elastic roll when voids appear on the surface of the cylinder.
When the outer layer cylinder includes voids therein, stress concentration takes place in portions having the voids, and the elastic roll may be broken.
On the other hand, each of Japanese Patent Laying-Open No. 8-166011, Japanese Patent Publication No. 62-40476, Japanese Patent Publication No. 48-37337 and Japanese Patent Laying-Open No. 56-4419 discloses a conventional method of forming a cylindrical body by centrifugal molding. It is known that voids can be effectively removed by centrifugation and a cylindrical body also excellent in cylindricity can be formed according to such centrifugal molding.
Every conventional method of forming a cylindrical body by centrifugal molding concentrates a filler to a desired position through centrifugation.
Such centrifugal molding has the following problems: In general, a reinforcing filler has such large specific gravity that the filler tends to concentrate to the outer surface side when subjected to centrifugal molding.
When the filler concentrates to the outer surface side, the hardness of the cylindrical body is increased on the surface and reduced toward the inner diameter side. Further, no homogeneous physical property can be attained in the thickness direction.
Therefore, the hardness or the physical property varies as the cylindrical body is cut or ground, and it is difficult to finish a roll defined in size to desired hardness or a desired physical property.
When the filler concentrates to the outer surface side, further, the filler is heterogeneously dispersed in the radial direction. In a roll rotating at a high speed with application of a load in a used state, therefore, a portion containing a small amount of filler disadvantageously tends to locally cause internal heat build-up when an inorganic filler is employed. When such internal heat build-up progresses, the roll may be broken.